Over the last three years it has become known to investigate and exploit redox enzyme systems by electrochemical methods. These involve use of the enzyme and a substrate which is caused to react by the enzyme. The existence or amount of the reaction is measured at an electrode using a mediator compound to transfer electrons from the reaction to the electrode.
A typical example is the system glucose/glucose oxidase/ferrocene (as mediator), as described in commonly owned U.S. Pat. No. 4,711,245 issued on U.S. Ser. No. 607,699, filed May 7, 1984. In a suitable circuit an electrode in contact with such a system will detect a charge, transferred from the enzyme by the mediator. A typical use of such a system is for the selective detection or measurement of blood glucose level in whole blood by an electrode on which layers, or a mixture, of mediator and enzyme are immobilised.
In practice the various components of such a system can be located on the electrode or in the contacting medium; moreover, the system can be used as a test either for substrate or for enzyme or for mediator levels. Elaboration of the basic concepts involves for example the variation of such levels by immunological or nucleic-acid-probe reactions and thus using the system in immunological assay or in DNa/RNA sequencing investigations.
All of the above systems, however, are indirect to the extent that they rely upon a mediator, e.g. ferrocene to transfer the charge from the enzyme molecule to the electrode itself.